Greetings. If you gave him the tax exemption, I cannot imagine why you would be worried about breaching the separation agreement, since he is benefitting from your breach and has consented to the same (assuming that your behavior was a breach).
As far as the car insurance, I would just e-mail your ex and explain in writing what happened. Keep a copy of the e-mail in case he sues you for the same. Best of luck.
Janet L. Fritts
Attorney at Law
4101 Lake Boone Trail, Suite 200
Raleigh, North Carolina 27607
The response posted above is based upon the limited factual information made available and is not intended as a full and complete response to the question. The only reliable manner to obtain complete and adequate legal advice is to consult with an attorney, fully explain your situation, and allow the attorney sufficient opportunity to research the applicable law and facts required to render an accurate opinion. The basic information provided above is intended as a public service but a full discussion with an attorney should be undertaken before taking any action.